The overall objective of this project is the characterization of the IgM class of immunoglobulins with emphasis on the relationship between structural features and biological properties. Previous studies have considered the number and location of the IgM antibody active sites and the role of the constituent polypeptide chains in their formation. This phase of the project will focus on the mechanisms and structures involved in the assembly of the 19S IgM molecule from the 7S monomer (IgMs). Two approaches will be utilized. The first will examine the interaction of the IgMs and J chain using reactants isolated from Waldenstrom's proteins. The studies will seek to define the obligatory role of J chain in the reassembly process, the specificity of its incorporation into the polymer and the relationship of the reassembled molecules to the native protein. The latter two goals will be achieved by isolating the products and characterizing such structural features as molecular weight, subunit and J chain content, site of J chain attachment and location of intersubunit bonds. The complementarity between the J and micron chains will be further examined using a monomeric Fc micron fragment. The second approach involves defining the structures that distinguish intracellular IgMs from the IgMs present in the extracellular protein using the MOPC 104E mouse tumor. In addition to basic physicochemical properties, the studies will endeavor to establish the number and distribution of free sulfhydryl groups and disulfide bonds in the intracellular IgMs. An effort will be made to determine the relative strength of the disulfide bonds and whether the bonds differ from those in the extracellular product. Other structural features to be considered are antigenic differences and expression of the antibody active site.